Physiol. Res. 52: 599-606, 2003

Modulation of Ionizing Radiation-Induced Apoptosis and Cell Cycle Arrest by All-Trans Retinoic Acid in Promyelocytic Leukemia Cells (HL-60)


1Department of Medical Biochemistry, Faculty of Medicine Hradec Králové, Charles University, Prague, 2Institute of Radiobiology and Immunology, Purkyně Military Medical Academy Hradec Králové, 3Institute of Clinical Immunology and Allergology, University Hospital, Hradec Králové, and 4Department of Military Medical Service Organization, Purkyně Military Medical Academy Hradec Králové, Czech Republic

Received April 15, 2002
Accepted October 16, 2002

Acute promyelocytic leukemia is characterized by a block of myeloid differentiation. The incubation of cells with 1 μmol/l all-trans retinoic acid (ATRA) for 72 h induced differentiation of HL-60 cells and increased the number of CD11b positive cells. Morphological and functional changes were accompanied by a loss of proliferative capacity. Differentiation caused by preincubation of leukemic cells HL-60 with ATRA is accompanied by loss of clonogenicity (control cells: 870 colonies/103 cells, cells preincubated with ATRA: 150 colonies/103 cells). D0 for undifferentiated cells was 2.35 Gy, for ATRA differentiated cells 2.46 Gy. Statistical comparison of clonogenity curves indicated that in the whole range 0.5-10 Gy the curves are not significantly different, however, in the range 0.5-3 Gy ATRA differentiated cells were significantly more radioresistant than non-differentiated cells. When HL-60 cells preincubated with 1 μmol/l ATRA were irradiated by a sublethal dose of 6 Gy, more marked increase of apoptotic cells number was observed 24 h after irradiation and the surviving cells were mainly in the G1 phase of the cell cycle, while only irradiated cells were accumulated in G2 phase. Our results imply that preincubation of cells with ATRA accelerates apoptosis occurrence (24 h) after irradiation by high sublethal dose of 6 Gy. Forty-eight hours after 6 Gy irradiation, late apoptotic cells were found in the group of ATRA pretreated cells, as determined by APO2.7 positivity. This test showed an increased effect (considering cell death induction) in comparison to ATRA or irradiation itself.

Key words
Apoptosis • All-trans retinoic acid • Ionizing radiation • HL-60 cells

Reprint requests
MUDr. Martina Mareková, Ph.D., Dept. of Medical Biochemistry, Faculty of Medicine Hradec Králové, Charles University Prague, Šimkova 870, 500 01 Hradec Králové, Czech Republic, e-mail:

© 2003 by the Institute of Physiology, Czech Academy of Sciences